We propose to investigate the mechanism by which the release of endogenous catecholamines mediates the potent cardiovascular effects of the carboxylic ionophores. The factors affecting catecholamine release from isolated cell preparations of adrenal medulla as well as from the heart itself will be evaluated. These studies will be extended to examination of the cell biology of the chromaffin cell and its regulation in order to gain better understanding of the parameters controlling cardiac function. This will entail resolving the subcellular organelles of the chromaffin cell by new combinations of differential sedimentation and density gradient centrifugation. The bioenergetic properties of the chromaffin granules in particular will be examined in depth. Individual protein species of the organelle fractions, characterized by the enzyme marker technique, will be identified by resolution two dimensional gel electrophoresis coupled with the binding of specific inhibitors. These techniques will be used to chart the sequence of events of the processing of membrane proteins during exocytosis and granule membrane retrieval. Protein homologies with other exocytotic granules will be examined in order to identify those membrane proteins which play a primary role in the exocytotic process in contradistinction to those proteins involved in the specialized functions of the chromaffin cell.